Supreme Court Associate Justice John Paul Stevens has made it clear that he will retire either this year or next, probably sooner rather than later. His retirement will set the stage for a new partisan battle in Washington, and analyses of whom the President may nominate to replace him are already appearing in the media, such as this excellent Politico article.

Although the average voter may not understand this well or think about it much, one of the most significant things a president does is nominate federal judges and defend them during the Senate confirmation process. Since federal judges have life tenure, the ones a president places on the bench will influence the country for many years after he has left office.

The justices a president nominates for the Supreme Court have massive influence, of course, but presidents also nominate judges at other levels. In addition to specialized courts created by statute, there are hundreds of so-called Article III judges authorized by the Constitution, with their numbers and jurisdiction set by Congress. While the nine justices of the Supreme Court get the most public attention, there are also 179 court of appeals judges, 678 district court judges, and nine judges of the Court of International Trade.

Each year the Supreme Court receives about 7,000 requests for appeals and over 1,000 applications of other kinds. The vast majority of these are declined by the Court, in effect leaving the decision being appealed in force. The Court issues only about 150 significant decisions each term. It’s easy to see that while the Supreme Court is where the high-profile drama takes place, the thousands of decisions made by federal district courts, some of them appealed to the courts of appeal, are where the federal courts really have an impact on citizens.

The Supreme Court, however, is where landmark decisions are made involving interpretations of the Constitution, and that’s where a president has the potential to literally shape the meaning of the Constitution long after he’s left the scene.

Justice Stevens is by tenure the senior justice on the present Court and one of the longest-serving in history. He’s also the de facto leader of the four-member liberal bloc on the Court, which also includes Associate Justices Ruth Bader Ginsburg, Sonia Sotomayor, and Stephen Breyer.

The conservative bloc, also with four justices, includes Chief Justice John Roberts and Associate Justices Antonin Scalia, Clarence Thomas, and Samuel Alito.

The swing vote is Associate Justice Anthony Kennedy, generally considered a moderate conservative. It’s his vote that often results in a case being decided by a liberal or a conservative majority.

There’s no doubt that President Obama will nominate a liberal to replace Stevens and to fill any other open seat on the Court. The only question is how liberal the nominees will be. But conservatives don’t need to worry about it too much. It’s likely that Obama will have the opportunity to nominate replacements only for the liberal judges now on the court. It’s unlikely that the conservative justices, who tend to be younger, will leave the Court during Obama’s tenure, unless there are unexpected resignations or accidental or natural deaths. However, there are two possibilities — Scalia, 74 and Kennedy (the swing vote), 73. If Obama has the chance to nominate their replacements, he could have a major influence on the future direction of the Court.

So the battle looms, and it may come before the mid-term election in November. With the Republicans now holding 41 seats in the Senate, the confirmation battle could be long and bloody, and judging by the level of partisanship that prevails in Washington, it’s likely to be. On balance, that probably would cause more problems for the Democrats than for the Republicans in November, and for that reason Obama might ask Stevens not to resign before the election. However, Stevens has indicated that he’d like to resign in time for his replacement to be seated when the next term begins in October 2010. We should know this month what he decides to do.

An interesting point: There are no constitutional qualifications to be a federal judge at any level, beyond presidential appointment and Senate confirmation. Judges, including Supreme Court justices, don’t even have to be lawyers, although by tradition they are. Technically speaking, you or I or your local plumber could become a Supreme Court justice. The idea that you or your plumber could sit on the Court bothers me a lot. I, on the other hand, would make a great justice!